Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

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Query: EC:3.4.21.5 (thrombin)
33,306 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The interaction of platelets with damaged vessel walls leads to the formation of platelet-fibrin thrombi and may also contribute to the development of atherosclerotic lesions because platelets adherent to exposed collagen release a mitogen that stimulates smooth muscle cell proliferation. The first step in thrombus formation, platelet adherence to an injured vessel wall, can be studied quantitatively by the use of platelets labeled with 51chromium. In these investigations, rabbit aortas were damaged by passage of a balloon catheter and segments of the aortas were everted on probes that were rotated in platelet suspensions. Collagen-coated glass cylinders were also used. Adherence was measured in a medium containing approximately physiologic concentrations of calcium, magnesium, protein and red blood cells. Conditions of testing influence the effect of non-steroidal anti-inflammatory drugs, sulfinpyrazone, and dipyridamole on platelet adherence. Aspirin and sulfinpyrazone were not inhibitory when tested in a medium with a 40% hematocrit; this indicates that products formed by platelets from arachidonate probably do not play a major part in the adherence of the first layer of platelets to the surface, although they may be involved in thrombus formation. Indomethacin, dipyridamole, prostaglandin E1, methylprednisolone and penicillin G and related antibiotics did inhibit platelet adherence although the concentrations required were higher than would likely be achieved in vivo upon administration to human patients. None of the non-steroidal anti-inflammatory drugs inhibited the release of granule contents from adherent platelets. Pretreatment of the damaged vessel wall with aspirin increased platelet adherence, presumably because it prevented the formation of PGI2 by the vessel wall. Platelet adherence to undamaged or damaged vessel walls was enhanced by prior exposure of the wall to thrombin. Platelet reactions with aggregating agents and platelet survival can be modified by changes in dietary lipids but there is very little evidence concerning the effects of lipids on platelet adherence. If some forms of dietary fat damage the endothelium, platelet interaction with the damaged area and release of the mitogen for smooth muscle cells would contribute to the development of atherosclerotic lesions.
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PMID:Drug effects on platelet adherence to collagen and damaged vessel walls. 36 49

Thrombin rapidly induces the formation of labeled phosphatidic acid from platelets prelabeled with [17C]arachidonate or 32PO34- and specifically decreases by 50--75% the content of phosphatidylinositol. Ionophore A23187 also stimulates phosphatidate labeling, but less effectively than thrombin. This effect on phosphatidic acid is blocked by increasing the levels of cyclic AMP by preincubation with dibutyryl cyclic AMP, cyclic AMP-phosphodiesterase inhibitors or prostacyclin. Indomethacin and eicosatetraynoic acid do not alter the production of phosphatidate, indicating independence from cyclooxygenase or lipoxygenase products. Increased turnover of [14C]- or [32P]phosphatidate occurs within 2--5 s after platelet activation by thrombin and is observed before endogenous, 14C-labeled arachidonate can be detected. The rate of phosphatidate formation parallels the induced rate of serotonin release. Release of [3H]serotonin is not affected by eicosatetraynoic acid. Phosphatidate production reflects the generation of diacylglycerol by C-type phospholipase degradation of phosphatidylinositol. Diacylglycerol and phosphatidic acid may participate in the membrane modification related to the early changes in platelet shape, release reactions or aggregation which occur on stimulation.
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PMID:Stimulation of phosphatidic acid production in platelets precedes the formation of arachidonate and parallels the release of serotonin. 37 88

Thrombocytin, a serine protease from Bothrops atrox venom, caused platelet aggregation and release of platelet constituents at a concentration of 10(-7) M and clot retraction at a concentration of 2 x 10(-9) M. Thrombocytin was slightly more active when tested on platelets in plasma than on washed platelets suspended in Tyrode--albumin solution. Thrombin was 5 times more active than thrombocytin when tested on platelets in plasma and 50 times more active when tested on washed platelets. The patterns or release induced by thrombocytin and thrombin were similar. Prostaglandin E1 (10(-5) M) produced complete inhibition of platelet release induced by thrombocytin and thrombin. Indomethacin (10(-4) M) was without any effect. Antithrombin III, in the presence of heparin, inhibited the action of thrombocytin on platelets and on a synthetic peptide substrate (Tos-Gly-Pro-Arg-pNA.HCl). formation of an antithrombin III--thrombocytin complex was demonstrated on NaDodSO4--polyacrylamide gel electrophoresis. Hirudin and alpha 1-antitrypsin did not inactivate thrombocytin. Thrombocytin had a low fibrinogen-clotting activity (less than 0.06% that of thrombin). Thrombocytin also caused progressive degradation of the alpha chain of human fibrinogen, and it cleaved prothrombin, releasing products similar to intermediate 1 and fragment 1 produced by thrombin. Thrombocytin activated factor XIII by limited proteolysis and increased the procoagulant activity of factor VIII in a manner analogous to that of thrombin.
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PMID:Thrombocytin, a serine protease from Bothrops atrox venom. 2. Interaction with platelets and plasma-clotting factors. 47 69

The initial shape change and subsequent aggregation of platelets in citrated rabbit platelet-rich plasma caused by ADP in vitro was inhibited by 15-hydroxyprostaglandin dehydrogenase. This inhibition was NAD-dependent and was also seen when shape change and aggregation were initiated by sodium arachidonate or by collagen. The aggregation of gel-filtered rabbit platelets by thrombin was not, however, affected by removal of 15-hydroxyprostaglandins. Indomethacin was found to inhibit ADP-induced aggregation but at a concentration (250 micron) much higher than that required to inhibit collagen-induced aggregation. Moreover the platelet release reaction had not taken place 3 min after ADP stimulation. The direct role 15-hydroxyprostaglandin production in ADP-induced aggregation of rabbit platelets is proposed. The involvement of 15-hydroxyprostaglandins in platelet aggregation caused by other inducers is also discussed.
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PMID:The role of prostaglandins in the ADP-induced aggregation of rabbit platelets shown by the use of 15-hydroxyprostaglandin dehydrogenase. 70 1

1. The A23187-induced secretion of preabsorbed serotonin from human blood platelets at 37 degrees C is studied. Preincubation at the same temperature before the addition of ionophore is necessary for maximal release induction. When total incubation time is kept constant, longer time with ionophore results in a smaller decrease in the level of metabolic ATP and increase in metabolic ATP and increase in metabolic IMP. This coincides with the reduction in secretion, but statistical treatment of the results suggests that the reduced secretion only partially explains the reduced drop in metabolic ATP, and that therefore a resynthesis of metabolic ATP from IMP may have taken place. 2. In some experiments induction of secretion takes place over a very narrow range of ionophore concentration. 3. When K+ substitutes for Na+ in the extracellular medium, the need for preincubation for maximal secretion becomes less evident, and at times is abolished, while there is still a significant increase in the metabolic ATP level by prolonged incubation with ionophore. 4. A reduction in secretion is observed with metabolic blockers when the ionophore is added after preincubation, but to a much less degree than when secretion is induced by thrombin, in spite of a great reduction in the level of metabolic ATP. This may partly be explained by the increase in secretion induction by A23187 in the presence of inhibitors when the ionophore is added in the cold, suggesting that the inhibitor may cause "weakening" of the platelets' "resistance" to induction of secretion by ionophore. 5. When the effect of Ca2+ and of Mg2+ on the level of intermediates of the TP leads to hypoxanthine conversion is studied, it is evident that the addition of Ca2+ causes enhanced IMP accumulation and a reduction in the level of inosine plus hypoxanthine, while Mg2+ has the opposite effect. This suggests that the two metals affect the enzymes of the IMP leads to hypoxanthine conversion differently. 6. Indomethacin inhibits secretion induced by A23187, suggesting that prostaglandin intermediates may amplify the ionophore-induced release. The adenine nucleotide metabolism is not affected. 7. The results indicate that there is an indirect, rather than direct, link between the major metabolic changes and the secretion induced by A23187, but that the ionophore may cause intracellular changes which are not connected to its effect as release inducer.
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PMID:Metabolic aspects of the secretion of stored compounds from blood platelets. V. Effect of ionophore A23187 on washed platelets. 79 62

1 Gas chromatographic and radio-isotope labelling techniques have been used to establish the origin of the arachindonic acid used by the platelet cyclo-oxygenase for the synthesis of pro-aggregatory prostaglandin endoperoxide derivatives. 2 Measurements of total platelet arachidonate content indicated that more than 95% is esterified in the phosphatide fraction of the cells. 3 During aggregation by collagen or thrombin as much as 80% of the total platelet arachidonate may be liberated and transformed by the platelet enzymes into hydroxyacids and other more polar compounds. 4 The phosphatidylethanolamine, phosphatidylcholine and phosphatidylinositol fractions are major sources of the arachidonate thus used. 5 Indomethacin, which prevents platelet aggregation by inhibiting the cyclo-oxygenase, did not affect this release of arachidonate from the phosphatides but did prevent the transformation of arachidonate to endoperoxide derivatives. 6 Mepacrine, a drug which possesses weak anti-phospholipase activity in platelets, also prevents aggregation by collagen or thrombin, but seems to do so by preventing substrate release from the phosphatide fraction. 7 It is suggested that phospholipase A2 plays a key role in the initial events during platelet aggregation induced by collagen.
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PMID:The distribution and metabolism of arachidonic acid in rabbit platelets during aggregation and its modification by drugs. 83 23

Formation of prostaglandin D2 (PGD2) during the aggregation of platelets was determined, employing a specific bioassay. PGD2 was synthesized in human platelet rich plasma (PRP) in response to thrombin, collagen and epinephrine. Indomethacin pretreatment abolished the biosynthesis of PGD2. When thrombin treated PRP was incubated for different periods of time and denatured in the presence of SnCl2 to prevent the formation of PGD2 from endoperoxides during the extraction procedure, PGD2 formation was noted within the first minute of incubation and reached a peak level after 4 minutes. PGD2 from thrombin stimulated PRP was conclusively identified by gas chromatography-mass spectrometry. The formation of PGD2 during platelet aggregation could represent a mechanism of feedback inhibition of aggregation.
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PMID:Biosynthesis of prostaglandin D2. 1. Formation of prostaglandin D2 by human platelets. 84 30

Prostaglandins E2 and F2alpha are present in the culture medium of methylcholanthrene-transformed mouse BALB/3T3 cells. The production of these prostaglandins is stimulated when the cells are incubated in the presence of serum, arachidonic acid, thrombin, and bradykinin, or if they are mechanically manipulated. Whereas the appearance of prostaglandins resulting from the latter four treatments is complete in several minutes, in the presence of serum the prostaglandin levels are still increasing ever after 2 hours. Stimulation by all of these treatments is additive. Indomethacin inhibits these stimulations, suggesting that the production of prostaglandins results from de novo biosynthesis.
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PMID:Stimulation of prostaglandin biosynthesis by vasoactive substances in methylcholanthrene-transformed mouse BALB/3T3. 94 51

The endoperoxide prostaglandin G2 (PGG2) induced platelet aggregation as well as the platelet release reaction (release of ADP and serotonin) when added to human platelet-rich plasma. Formation of a metabolite of PGG2 [8-(l-hydroxy-3-oxopropyl)-9,12L-dihydroxy-5,10-heptadecadienoic acid] and a lipoxygenase product [12L-hydroxy-5,8,10,14-eicosatetraenoic acid] accompanied the release reaction caused by aggregating agents such as collagen, ADP, epinephrine, and thrombin. Indomethacin inhibited the release reaction and PGG2 formation induced by these agents but had no effect on PGG2-induced release reaction. The aggregating effect of PGG2 was abolished by furosemide, which is a competitive inhibitor of ADP-induced primary aggregation. These data indicate that the aggregating effect of PGG2 is due to release of ADP and that PGG2 synthesis is required for induction of the release reaction by various aggregating agents. A subject with a hemostatic defect due to abnormal release mechanism [decreased aggregation with epinephrine (second wave) and collagen and normal platelet ADP] had a deficiency of the cyclo-oxygenase that catalyzes formation of PGG2. Normal aggregation and release reaction were obtained with added PGG2. Ii is concluded that the endoperoxide (PGG2) is essential in normal hemostasis because of its role in initiating the release reaction required for aggregation by collagen and the second wave of aggregation caused by, e.g., ADP.
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PMID:Physiological role of an endoperoxide in human platelets: hemostatic defect due to platelet cyclo-oxygenase deficiency. 105 17

The effect of thrombin on mesangial cell function was investigated. Thrombin caused a dose-dependent increase in [3H] thymidine incorporation (EC50 = 0.36 +/- 0.09 U/ml), intracellular calcium [(Ca++)i] mobilization (EC50 = 1.9 +/- 0.5 U/ml) and prostaglandin E2 (PGE2) production (EC50 = 0.25 +/- 0.02 U/ml) in rat glomerular mesangial cells. These effects were blocked by the thrombin inhibitor, hirudin (KB = 10.4 +/- 0.2 nM). The role of (Ca++)i mobilization and arachidonate metabolism in thrombin-stimulated proliferation was tested by the addition of the calcium channel blocker, nifedipine, and the cyclooxygenase inhibitor, indomethacin, to mesangial cell cultures. Indomethacin, at doses that completely inhibited the thrombin-mediated production of PGE2, had no significant effect on proliferation. The Ca++ channel blocker, nifedipine, inhibited both PGE2 production and [3H] thymidine incorporation in a dose-dependent fashion, but only at concentrations considered nonspecific. In addition to its effects on PGE2, thymidine incorporation and Ca++ mobilization, thrombin caused mesangial cell contraction as determined by a substrate distortion technique. This effect was not inhibited by indomethacin. These results indicate that thrombin can alter mesangial cell function in vitro.
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PMID:Effect of thrombin on proliferation, contraction and prostaglandin production of rat glomerular mesangial cells in culture. 140 2


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